Only 40% of the 21 gun murders investigated by Operation Trident last year have been solved, half the normal clear-up rate for murders.

Gun crime is already under the spotlight in London with a double murder among the shootings so far this year, and the case of a 19-year-old woman shot in the head for her mobile phone.

'Narcissistic criminals'

Last year, the number of armed street robberies rose to 776 from 500 the year before and police are currently seizing 50 guns every month.

In addition to the fatal shootings, there were also 67 attempted murders and another 80 shootings resulting in minor injury or criminal damage.

But the mayor will speak of the courage of Trident officers, who arrested 441 people and seized 620kg of drugs last year, describing their bravery as "unprecedented".

We have seen people shot because they have made a sarcastic remark about someone's haircut

Commander Alan BrownOperation Trident

Mr Livingstone will tell the conference: "I want to pay tribute to those black heroes who have built a partnership with the police within their community and said enough is enough.

"Their contribution and courage needs to be recognised because they continue to live in those areas where Trident crimes are most prevalent."

He will also warn of the danger of excluding young black boys from school.

"If the last time a young black male sees the inside of a classroom is at the age of 12 then we are preparing for not only the possibility of a life of crime, but in some cases the inevitability of it."

Commander Alan Brown, the head of Operation Trident, admitted there had been a "significant rise" in shootings since September last year which was "very worrying".

Extreme violence

He said the drug and gun culture was producing an "incredibly narcissistic" generation of violent young criminals.

"Their reaction to any act of what they see as disrespect is extreme violence.

"We have seen people shot because they have made a sarcastic remark about someone's haircut or stood on someone's foot in a nightclub and not said sorry."

And Commander Brown insisted police were "very much on the case" in dealing with the increased opportunities for drug smuggling offered by extra flights from Jamaica to the UK.

In March, Air Jamaica will boost its number of flights into Heathrow from five to nine with an additional two flights to Manchester.

Customs' plans

It has been estimated that one in 10 passengers on flights from Jamaica are cocaine mules, swallowing packets of drugs to deliver to dealers in the UK.

Mr Brown said the new flights would "undoubtedly provide additional opportunities for couriers to come into this country".

But he added: "I'm confident of the measures being put in place by customs, the Jamaican authorities, Air Jamaica and BA."

Measures include drawing up profiles of potential couriers and identifying individuals in Jamaica who may be recruited by gangs.

The commander denied the rise in London's gun crime was linked to officers being removed from normal duties to carry out anti-terrorist patrols since 11 September.